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Commit 9d2e3489 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux 

Pull arm64 fixes from Will Deacon:
 "Catalin's out enjoying the sunshine, so I'm sending the fixes for a
  couple of weeks (although there hopefully won't be any more!).

  We've got a revert of a previous fix because it broke the build with
  some distro toolchains and a preemption fix when detemining whether or
  not the SIMD unit is in use.

  Summary:

   - Revert back to the 'linux' target for LD, as 'elf' breaks some
     distributions

   - Fix preemption race when testing whether the vector unit is in use
     or not"

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64: neon: Fix function may_use_simd() return error status
  Revert "arm64: Use aarch64elf and aarch64elfb emulation mode variants"
parents e6ef7607 2fd8eb4a

arch/arm64/Makefile

+4 −2
Original line number Diff line number Diff line
@@ -60,13 +60,15 @@ ifeq ($(CONFIG_CPU_BIG_ENDIAN), y) 
KBUILD_CPPFLAGS	+= -mbig-endian

CHECKFLAGS	+= -D__AARCH64EB__

AS		+= -EB

LDFLAGS		+= -EB -maarch64elfb

# We must use the linux target here, since distributions don't tend to package

# the ELF linker scripts with binutils, and this results in a build failure.

LDFLAGS		+= -EB -maarch64linuxb

UTS_MACHINE	:= aarch64_be

else

KBUILD_CPPFLAGS	+= -mlittle-endian

CHECKFLAGS	+= -D__AARCH64EL__

AS		+= -EL

LDFLAGS		+= -EL -maarch64elf

LDFLAGS		+= -EL -maarch64linux # See comment above

UTS_MACHINE	:= aarch64

endif

arch/arm64/include/asm/simd.h

+7 −12
Original line number Diff line number Diff line
@@ -29,20 +29,15 @@ DECLARE_PER_CPU(bool, kernel_neon_busy); 
static __must_check inline bool may_use_simd(void)

{

	/*

	 * The raw_cpu_read() is racy if called with preemption enabled.

	 * This is not a bug: kernel_neon_busy is only set when

	 * preemption is disabled, so we cannot migrate to another CPU

	 * while it is set, nor can we migrate to a CPU where it is set.

	 * So, if we find it clear on some CPU then we're guaranteed to

	 * find it clear on any CPU we could migrate to.

	 *

	 * If we are in between kernel_neon_begin()...kernel_neon_end(),

	 * the flag will be set, but preemption is also disabled, so we

	 * can't migrate to another CPU and spuriously see it become

	 * false.

	 * kernel_neon_busy is only set while preemption is disabled,

	 * and is clear whenever preemption is enabled. Since

	 * this_cpu_read() is atomic w.r.t. preemption, kernel_neon_busy

	 * cannot change under our feet -- if it's set we cannot be

	 * migrated, and if it's clear we cannot be migrated to a CPU

	 * where it is set.

	 */

	return !in_irq() && !irqs_disabled() && !in_nmi() &&

		!raw_cpu_read(kernel_neon_busy);

		!this_cpu_read(kernel_neon_busy);

}



#else /* ! CONFIG_KERNEL_MODE_NEON */